Carpometacarpal arthritis of the thumb – rhizarthrosis

ANATOMY

Key joint of the thumb

Saddle-shaped joint

Biconcavo-convex shape

Joint compression force = 12kg (120kg for strong grip)

3 Main ligamentous stabilisers:

1. Volar or Beak ligament

• most NB ligament - primary static stabiliser
• very strong
• prevents dorsal translation of the MC in key pinch
• Allows rotational motion
• Evolutionary remnant of the bony palmar beak
• synonyms = volar oblique lig., anterior oblique lig.(AOL), volar CMC lig., deep ulnar lig.
• Important in Bennett's Fractures

2. Dorsal ligament

• thin & reinforced by APL

3. Lateral ligament

• broad band running from lateral surface of trapezium to 1st MC base

PATHOPHYSIOLOGY

Described by Pelligrini (1991) following examination of cadaveric & surgical specimens.

Attritional changes in the beak lig. leads to destabilisation of the 1st CMCJ causing degenerative changes.

These changes initially occur in the palmar contact areas of the joint.